In a General Packet Radio Service (GPRS) system, a handover across Radio Access Network (RAN) boundaries may be necessary when a communication unit such as a mobile station (MS), user equipment (UE), user entity (UE) or the like is moving between RANs. In a conventional inter-RAN handover environment such as in a second generation Global System for Mobile (GSM) system or the like, an external or inter-RAN handover typically involves a Mobile Switching Center (MSC) to support the RAN-to-RAN communications required for the handover.
Conventional, second generation GSM mobile networks, use the MSC to provide an interface with the public fixed network such as the Public Switched Telephone Network (PSTN), or the like. From the perspective of the fixed network, the MSC is just another switching node. From the perspective of the mobile network however, switching or handover is more complicated since the MSC needs to know where the MS is currently located and where it may be heading. As is well known to those of ordinary skill in the art, a GSM system accomplishes location updating and call routing to the MS by using the Home Location Register (HLR) and the Visitor Location Register (VLR).
When the MS notices that the location-area broadcast information is different from that previously stored in the MS memory, by monitoring, for example, the Broadcast Control Channel (BCCH), an update request and the International Mobile Subscriber Identity (IMSI) or previous Temporary Mobile Subscriber Identity (TMSI) is sent to the VLR via the MSC. When a new MSC is encountered, a new Mobile Station Roaming Number (MSRN) is allocated and sent to the HLR associated with the MS by the VLR. The MSRN is a regular telephone number which rather than being assigned to a single user is part of a pool of numbers. The MSRN is used to route the call to the new MSC and is subsequently translated to the IMSI of the mobile. The HLR sends back the necessary call-control parameters, and also sends a cancel message to the old VLR, so that the previous MSRN can be reallocated. Finally, a new TMSI is allocated and sent to the mobile for identification in future paging or call requests.
Conducting handovers using the MSC can give rise to limitations associated with, for example, latency. Further, while the MSC, HLR, VLR model was developed with a circuit switching model in mind, third generation (3G) systems support high speed packet switching. Moreover, since the MSC is not involved in the handover activities of packet services in accordance with 3G system associated with, for example, Universal Mobile Telecommunications Services (UMTS), CDMA 2000 and the like, other solutions are needed to accomplish handover of packet-based calls or sessions, particularly real time packet-based calls or sessions associated with providing support for voice and/or multimedia services.